PyQt5 bug in font settings

[ullix]

I believe I found a bug in PyQt5 (or QT?) , surfacing only under 
Windows, perhaps only Win10

The problem: A font may be set, and confirmed by PyQt5 to be in use, yet 
the actual font is a completely different one. I noticed this when I 
defined a fixed width font, but became a proportional font, despite 
PyQt5 telling it is Courier New.

More details already reported here:

https://stackoverflow.com/questions/64213031/python3-with-pyqt5-on-win10-ignores-font-settings